The present invention relates to a process for the preparation of a feedstock for a hydroprocessing unit, wherein said feedstock is based on crude oil containing asphaltenes.
Refineries are facing the challenges of oil becoming heavier and worse. Asphaltenes are the most difficult components in processing of heavy oils, which is a complex macromolecule that contains the majority of impurities such as S, N, Ni and V. The composition, structure and concentration of asphaltenes highly determine the quality and processing effect of heavy oil to a certain degree. Hydroprocessing is one of the most effective technologies of heavy oil processing. However, during hydroprocessing carbon deposit and pore blocking on the surface of catalysts are easily to occur because of the congregation and coking of the constituents of asphaltenes, which can greatly shorten the operational life span of the catalyst and the running period of the plant. These high molecular weight, large multi-ring aromatic hydrocarbon molecules or associated heteroatom-containing (e.g., S, N, O) multi-ring hydrocarbon molecules in heavy oils are called asphaltenes. A significant portion of the sulphur is contained within the structure of these asphaltenes. Due to the large aromatic structures of the asphaltenes, the sulphur can be refractory in nature and can be difficult to remove.
Asphaltenes are thus present in the crude oil along with other components which aid in keeping them in dissolved state. In the process of crude distillation, most of these other components present in the lower boiling ranges than asphaltenes are removed from the crude oil. This concentrates the asphaltenes in the residue. Depending on the solubility of asphaltenes in the crude oil residue, it can crash out of the solution due to aggregation and precipitate as solids. Precipitated asphaltenes in downstream hydroprocessing units leads to catalyst fouling and lower time-on-stream for the hydroprocessing reactors.
US patent application No 2007/090018 relates to a process comprising: (i) obtaining a hydroprocessed effluent from a resid hydroprocessing unit, wherein the effluent comprises 650 [deg.] F.+(343 [deg.] C.+) resid; (ii) steam cracking substantially all of the effluent to obtain a product comprising olefins. Crude or resid-containing fraction thereof, particularly atmospheric resid, vacuum resid, or any asphaltene-containing refinery or chemical intermediate stream are a feed to the hydroprocessor. The product of each of the steam crackers is sent to the steam cracker product recovery section, where various products may be recovered by separation. Tar from the product recovery unit, heated to a temperature of from about 100 [deg.] C. to about 200 [deg.] C. to maintain fluidity, and containing substantially no metals, and comprising very little asphaltenes and other 1050 [deg.] F.+ materials, is passed to the hydroprocessor, wherein the tar is being diluted with the feed to the hydroprocessor. The objective of this reference is to maximize conversion of asphaltene by steam cracking and recycling it for hydroprocessing and utilizes segregation of asphaltenes.
WO91/17230 relates to a process for the production of normally gaseous mono- and di-olefins, particularly ethylene, propylene and butadiene, by thermally cracking a hydrocarbon feedstock in the presence of steam at elevated temperatures which involves introducing a hydrogen donor material, such as hydrotreated steam cracked tar oils, into a stream of steam cracked effluent at or downstream of the point where the furnace effluent reactions are quenched so as to prevent thermal degradation reactions of the steam cracked liquids.
US Patent application No 2011/005970 relates to a cracking process that treats steam cracker tar fractions by exposure to heat in the presence of hydrogen donor compounds to prevent or decrease formation of at least a portion of high boiling molecules, including asphaltenes and/or asphaltene precursors, within the effluent stream, comprising: a) feeding a hydrocarbon feedstock having a final boiling point above 260° C. to a steam cracking furnace containing a radiant section outlet producing a steam cracker tar-containing effluent, b) adding a hydrogen donor-rich hydrocarbon stream comprising naphthenic compounds to at least a portion of the steam cracker tar-containing effluent while the tar-containing effluent is at a temperature of from 200° to 850° C. to form a mixture comprising hydrogen donor-rich hydrocarbons and steam cracker tar-containing effluent; and c) separating the mixture into i) at least one tar-lean product containing a first tar; and ii) a tar-rich product containing a second tar, the tar-rich product having a final boiling point above the final boiling point of the at least one tar-lean product.
US patent application No 2007/295640 relates to a composition comprising an asphaltenes solvent and a viscosity reducing agent, the asphaltenes solvent and viscosity reducing agent present in a ratio so as to substantially reduce viscosity of an asphaltenes-containing material while substantially negating deposition of asphaltenes either in a reservoir, in production tubing, or both when mixed or otherwise.
WO2013/033293 relates to a process for producing a hydro processed product, comprising: exposing a combined feedstock comprising a heavy oil feed component and a solvent component to a hydroprocessing catalyst to form a hydro processed effluent, separating the hydroprocessing effluent to form at least a liquid effluent and fractionating a first portion of the liquid effluent to form at least a distillate product, wherein the solvent comprises at least a portion of the distillate product, at least 90 wt. % of the at least a portion of the distillate product having a boiling point in a boiling range of 149 DEG C. to 399 DEG C.
Cracked distillate is a by-product obtained in the thermal cracking of a cracker feedstock, which by-product comprises a mixture of hydrocarbons with a boiling range of between 80 and 260 DEG C., at least 35 wt. % of which consists of unsaturated hydrocarbons. ‘Cracked distillate’ is also understood to be a fraction of unsaturated compounds that can be polymerised into a resin, obtained from distillation of coal tar. The liquid product of the cracking process is known as black oil. Black oil is highly aromatic and constitutes a valuable feedstock for the production of carbon black and for the manufacture of electrodes.
In a situation in which the commercial need for both cracked distillate and carbon black oil is decreasing new technical markets and end uses for these products need to be developed.
Not only carbon deposit and pore blocking on the surface of catalysts are unwanted phenomena but the presence of high amounts of sulphur in the feedstock as well. These sulphur-containing and/or nitrogen-containing organic compounds may compete for the active catalyst sites in the reaction zone in hydroprocessing units as a result of which hydrocracking reaction performance is affected.